Bachmann&#39;s bundle electrode for atrial defibrillation

ABSTRACT

An implantable system for the defibrillation of the atria of a patient&#39;s heart comprises (a) a first catheter configured for insertion into the right atrium of the heart; a first atrial defibrillation electrode carried by the first catheter and positioned to stimulate Bachmann&#39;s bundle, or positioned at the atrial septum of the heart (i.e., an atrial septum electrode); (b) a second atrial defibrillation electrode which together with the first atrial defibrillation electrode provides a pair of atrial defibrillation electrodes that are configured for orientation in or about the patient&#39;s heart to effect atrial defibrillation, and (c) a pulse generator operatively associated with the pair of atrial defibrillation electrodes for delivering a first atrial defibrillation pulse to the heart of the patient. The second electrode may be configured for positioning through the coronary sinus ostium and in the coronary sinus or a vein on the surface of the left ventricle, such as the great vein. An additional electrode configured for positioning in the superior vena cava, right atrium (including the right atrial appendage, or the right ventricle may also be included, and the pulse generator may be configured or programmed for concurrently delivering a first defibrillation pulse through the additional electrode and the atrial septum electrode, and a second defibrillation pulse through the atrial septum electrode and the second electrode. Electrode assemblies and methods useful for carrying out the invention are also disclosed.

RELATED APPLICATIONS

[0001] This application claims priority from U.S. patent applicationSer. No. 09/827,535, filed Apr. 6, 2001, which in turn claims thebenefit U.S. provisional application serial No. 60/196,722, filed Apr.13, 2000, the disclosures of both of which are incorporated by referenceherein in their entirety.

GOVERNMENT SUPPORT

[0002] This invention was made with Government support under NationalInstitute of Health grant HL-42760. The Government has certain rights tothis invention.

FIELD OF THE INVENTION

[0003] This invention relates to methods, apparatus, and catheters thatmay be used to administer a therapeutic electrical pulse, such as anatrial defibrillation pulse, to the heart of a patient in need of suchtreatment.

BACKGROUND OF THE INVENTION

[0004] Atrial fibrillation (AF) is the most common arrhythmia in humansand represents a significant public health problem. There are presently2.2 million cases of AF in the United States and approximately 160,000new cases diagnosed each year. AF is typically managed by a combinationof anti-arrhythmic drugs and external or internal electricalcardioversion. In addition, surgical compartmentalization orradiofrequency ablation of atrial tissue can be used. Unfortunately,long term success rates are low; AF recurrence is high with both drugtreatment and electrical cardioversion with internal and externalshocks.

[0005] Internal electrical cardioversion of AF remains an uncomfortabletherapy option for managing patients with AF. Even with recentadvancements, shock voltages necessary to defibrillate the atrial, whileconsiderably lower than that for the ventricles, are still beyond thepain threshhold. One reason high voltages may be necessary is that themain generator for AF is the left atrium and direct access to the leftatrium is problematic because of the risk of embolism. Typically, atrialdefibrillation lead locations are limited to right sided chambers (rightatrium and right ventricle) and venous structures accessible from theright side of the heart (coronary sinus).

[0006] To creat a trans-atrial shocking vector, the most common approachis to shock between one or more electrodes on the right side of theheart (right atrial appendage, superior vena cava, or right ventricle)to an electrode on the left side of the heart in the distal coronarysinus. The left atrium is also an important atrial chamber todefibrillate since (i) it can fibrillate independent of the rightatrium, (ii) mapping studies have shown that earliestsites of activationfollowing failed defibrillation arise from the left atrium for mostdefibrillation electrode configurations, (iii) early sites in or nearthe pulmonary veins have been shown to be responsible for the initiationof and early reoccurence of AF in many patients, and (iv) ablation ofright atrial structures alone has had poor success in terminating AF orpreventing its reoccurence. Nevertheless, there remains a need for meansof defibrillating the atria of a subject without unduly high energydefibrillation pulses that would be painful to the subject beingtreated.

SUMMARY OF THE INVENTION

[0007] A first aspect of the present invention is an implantable systemfor the defibrillation of the atria of a patient's heart. The systemcomprises (a) a first catheter configured for insertion into the rightatrium of the heart (in one embodiment preferably without extending intothe right ventricle of the heart); a first atrial defibrillationelectrode carried by the first catheter and positioned at Bachmann'sbundle or at the atrial septum of the heart (i.e., a Bachmann's bundleor an atrial septum electrode); (b) a second atrial defibrillationelectrode which together with the first atrial defibrillation electrodeprovides a pair of atrial defibrillation electrodes that are configuredfor orientation in or about the patient's heart to effect atrialdefibrillation, and (c) a pulse generator operatively associated withthe pair of atrial defibrillation electrodes for delivering a firstatrial defibrillation pulse to the heart of the patient. The secondelectrode may be configured for positioning through the coronary sinusostium and in the coronary sinus or a vein on the surface of the leftventricle, such as the great vein. As explained further below, anadditional electrode configured for positioning in the superior venacava, right atrium (including the right atrial appendage, or the rightventricle may also be included, and the pulse generator may beconfigured or programmed for concurrently delivering a firstdefibrillation pulse through the additional electrode and the atrialseptum electrode, and a second defibrillation pulse through the atrialseptum electrode and the second electrode.

[0008] A second aspect of the present invention is a catheter assemblyuseful for the defibrillation or cardioversion of a patient's heart. Theassembly comprises: (a) a first transveneous catheter configured forinsertion into the heart of the patient, the first transvenous catheterhaving a proximal end portion, a distal end portion, and an elongateintermediate portion therebetween, and with the first transveneouscatheter having a first electrode connected thereto; (b) a secondtransveneous catheter configured for insertion into the heart of thepatient, the second transveneous catheter having a proximal end portion,a distal end portion, and an elongate intermediate portion therebetween;and (c) a connecting member attached to the first transveneous catheter,with the connecting member connected to the second transveneous catheterintermediate portion.

[0009] A further aspect of the present invention is a method for thedefibrillation or cardioversion of the heart of a patient in needthereof while minimizing or reducing the voltage of the defibrillationpulses to be delivered. The method comprises the steps of: (a)positioning first and second defibrillation electrodes in operableassociation with the heart of the subject, the first and seconddefibrillation electrodes defining a gradient field in the heart, thegradient field including a region of the heart to be defibrillated; (b)positioning a third electrode in the gradient field between the firstand second electrodes; and then (c) concurrently delivering (i) a firstdefibrillation pulse between the first and third electrode and (ii) asecond defibrillation pulse between the second and third electrodes;with the first and second defibrillation pulses together effective todefibrillate the heart. The voltage required for each of the first andsecond defibrillation pulses is preferably less than the voltagenecessary for a single defibrillation pulse delivered between the firstand second electrodes that is effective to defibrillate the heart. One,two or three or more additional electrodes may be positioned between thefirst, second and third electrodes to further reduce the voltagerequired, with additional shocks being delivered concurrently betweenvarious combinations of the electrodes (typically between adjacentelectrodes).

[0010] A further aspect of the present invention is an implantablesystem for the defibrillation or cardioversion of a patient's heart. Thesystem comprises: (a) first and second defibrillation electrodesconfigured for positioning in operable association with the heart of thesubject, the first and second defibrillation electrodes when sopositioned defining a gradient field in the heart between the first andsecond electrodes and in a region to be defibrillated; (b) a thirddefibrillation electrode configured for positioning in the gradientfield between the first and second electrodes; and (c) a pulse generatoroperatively associated with the first, second and third defibrillationelectrodes and configured for concurrently delivering (a) a firstdefibrillation pulse between the first and third electrode and (b) asecond defibrillation pulse between the second and third electrodes. Thetwo pulses are together effective to defibrillate the heart. Preferably,the voltage required for each of the first and second defibrillationpulses is less than the voltage required for a single defibrillationpulse delivered between the first and second electrodes that iseffective to defibrillate the heart. Such an apparatus may be configuredto carry out the methods described above.

[0011] In preferred embodiments of the foregoing methods and systems,there is further provided first and second transveneous catheters,wherein the first, second and third electrodes are carried by the firstand second transveneous catheters, and wherein the first transveneouscatheter is fixed to the second transveneous catheter.

[0012] In particularly preferred embodiments of the foregoing methodsand systems, the first and second electrodes are carried by a firsttransveneous catheter, the first transveneous catheter having a proximalend portion, a distal end portion, and an elongate intermediate portiontherebetween. The third electrode is carried by a second transveneouscatheter, the second transveneous catheter having a proximal endportion, a distal end portion, and an elongate intermediate portiontherebetween. The second transveneous catheter distal end portion isconnected to the first transveneous catheter intermediate portionthrough a connecting member, as described in connection with catheterassemblies above. The third electrode is then, preferably, an atrialseptum electrode.

[0013] A further aspect of the present invention is an implantablesystem for the electrical treatment/defibrillation of the atria of apatient's heart, the system comprising: a first atrial therapeuticelectrode configured for stimulating Bachmann's bundle and forpositioning on or adjacent Bachmann's bundle along the superior aspectof the atrium and adjacent to the atrial septum; a second atrialelectrode which together with the first atrial electrode provides a pairof atrial electrodes; and a pulse generator operatively associated withthe pair of atrial electrodes for delivering an atrial defibrillation orother therapeutic pulse. Methods of delivering an atrial defibrillationpulse, or other therapeutic pulse, by positioning electrodes asdescribed above are a further aspect of the invention. The first atrialelectrode may be carried by a first catheter, with the first catheterconfigured for insertion into the right atrium of the heart, preferablywithout extending into the right ventricle of the heart. The secondatrial electrodes may be positioned as described in connection withsecond electrodes corresponding to or paired with atrial septumelectrodes as described herein.

[0014] A further aspect of the present invention is a method for theelectrical treatment or defibrillation of the atria of a patient'sheart, comprising the steps of: providing a set of atrial therapeuticelectrodes for defibrillating the patient's heart, or otherwiseadministering a therapeutic electric pulse to the patients heart, theset including a first atrial electrode positioned in the superior venacava of the patient; delivering a first therapeutic electric pulse suchas a defibrillation pulse to the atria of the heart, and then deliveringa second therapeutic electric pulse such as a defibrillation pulse pulseto the atria of the heart, wherein at least one of the first and secondpulses is delivered with the first atrial defibrillation electrode. Setsof atrial therapeutic or defibrillation electrodes that may be used tocarry out this method include but are not limited to the sets of atrialdefibrillation electrodes described herein. For example, the set ofatrial electrodes may further comprise a second atrial therapeutic ordefibrillation electrode positioned in the coronary sinus of the heart,and at least one of the first and second pulses may be delivered withthe second atrial electrode. In one embodiment, at least one of thefirst and second therapeutic pulses is delivered between the first andsecond therapeutic electrodes.

[0015] A further aspect of the present invention involves the balancingof peak amplitudes for defibrillating the atria or ventricles of apatient's heart, or otherwise delivering a therapeutic electric pulse tothe atria or ventricles of a patient's heart. The method comprises:delivering a first therapeutic electrical pulse such as a defibrillationpulse to the atria or ventricles of the heart, and then delivering asecond therapeutic electric pulse such as a defibrillation pulse to theatria or ventricles of the heart, wherein the total energy, or leadingedge peak voltage, of the second pulse is at least 90 or 95% of thetotal energy, or leading edge peak voltage, of the first pulse. Sets oftreatment electrodes that may be used to carry out this method includebut are not limited to the sets of atrial treatment electrodes describedherein. An apparatus configured to carry out this method (e.g.,employing two separate discharge capacitors operatively associated witha power supply and a controller, with the controller configured so thatthe first capacitor is discharged by the controller to administer thefirst pulse and the second capacitor is discharged by the controller toadminister the second pulse; or with a single capacitor havingsufficient storage capacity so that the aforesaid energy or voltagefeatures can be achieved through wave shaping through the controller) isa further aspect of the invention.

[0016] A still further aspect of the present invention is a transveneouscatheter for stimulating the heart of a patient at separate locationstherein, the catheter comprising: a catheter body having a proximalportion, an intermediate portion and a distal portion; a first electrodeconnected to the catheter body distal portion; a catheter appendagehaving a proximal portion and a distal portion, the appendage proximalportion connected to the catheter body intermediate portion; and asecond electrode connected to the appendage distal portion. In oneembodiment of the foregoing, the catheter body is configured forinsertion into the right ventricle of the heart. In a particularembodiment of the foregoing, the catheter body is configured forinsertion through the coronary sinus ostium and into the coronary sinusof the heart. The second electrode of the catheter may be an aterialelectrode, such as an atrial septum electrode or a Bachmann's bundleelectrode.

[0017] The foregoing and other objects and aspects of the presentinvention are explained in greater detail in the drawings herein and thespecification set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 illustrates a first embodiment of an implantable system ofthe present invention, in which the atrial septum electrode is atrans-septal electrode. The heart is shown in partial cut-away view,with the right atrium, the right ventricle, and a portion of the leftatrium being shown in cross section. The surface of the left ventricleis shown so that vessels on the surface of the ventricle that areaccessed through the coronary sinus (shown in dashed lines) may be seen.

[0019]FIG. 2 illustrates a second embodiment of an implantable system ofthe present invention, in which the atrial septum electrode is fixed tothe atrial septum by means of a terminal screw.

[0020]FIG. 3 illustrates a third embodiment of an implantable system ofthe present invention, in which the atrial septum electrode isincorporated into an expandable umbrella device which is opened withinthe right atrium to hold the electrode against the atrial septum.

[0021]FIG. 4 illustrates a fourth embodiment of an implantable system ofthe present invention, in which the atrial septum electrode is fixed tothe coronary sinus electrode to form a catheter assembly and facilitatethe holding of the atrial septum electrode against the atrial septum.

[0022]FIG. 5 illustrates a catheter assembly as used in FIG. 4, in whichthe first catheter is permanently fixed to the second catheter.

[0023]FIG. 6 illustrates an alternate embodiment of a catheter assemblyof the present invention, in which the first catheter is releasablyfixed to the second catheter by means of a retractable loop.

[0024]FIG. 7 illustrates a further alternate embodiment of a catheterassembly of the present invention, in which the first catheter isreleasably fixed to the second catheter by means of an elastic loop.

[0025]FIG. 8 illustrates a still further alternate embodiment of acatheter assembly of the present invention, in which the connectingmember is positioned on an intermediate portion rather than the distalportion of the first catheter.

[0026]FIG. 9 illustrates a still further alternate embodiment of animplantable system incorporating a catheter assembly of the presentinvention, in which the second catheter extends into the right ventricleand is fixed to the apex of the right ventricle by means of a terminalscrew.

[0027]FIG. 10 illustrates a further embodiment of a catheter assembly ofthe present invention, in which the second catheter includes anexpandable stent to further anchor the second catheter within a suitablevessel, such as a pulmonary artery.

[0028] FIGS. 11A-C schematically illustrate a technique for loweringshock voltage that may be used in conjunction with the instant inventionor other defibrillation techniques.

[0029]FIG. 12 schematically illustrates a technique for loweringventricular defibrillation voltage that implements the techniqueillustrated in FIGS. 11A-C.

[0030]FIG. 13 shows the ADFT leading edge voltage in experimentalanimals used to demonstrate the instant invention.. The leading edgevoltage of configuration A2 is significantly lower than the others(number shows the percent lower).

[0031]FIG. 14 shows the ADFT leading edge current in experimentalanimals used to demonstrate the instant invention. The leading edgecurrent of configuration A2 is significantly lower than the others(number shows the percent lower).

[0032]FIG. 15 shows the ADFT total shock energy in experimental animalsused to demonstrate the instant invention. The shock energy ofconfiguration A2 is significantly lower than the others (number showsthe percent lower).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention is explained in greater detail below. Thisdescription is not intended to be a detailed catalog of all thedifferent ways in which the invention may be implemented, or all thefeatures that may be added to the instant invention. For example,features illustrated with respect to one embodiment may be incorporatedinto other embodiments, and features illustrated with respect to aparticular embodiment may be deleted from that embodiment. In addition,numerous variations and additions to the various embodiments suggestedherein will be apparent to those skilled in the art in light of theinstant disclosure which do not depart from the instant invention.Hence, the following specification is intended to illustrate someparticular embodiments of the invention, and not to exhaustively specifyall permutations, combinations and variations thereof.

[0034] The terms “atrial septum electrode” or electrode positioned “atthe atrial septum”, as used herein, refer to an electrode that is, or isconfigured to be, inserted through the atrial septum (i. e., atrans-septal electrode), inserted into the atrial septum (i.e., insertedpartially into the septum without penetrating completely through theseptum), or substantially contacted to the surface of the atrial septum(typically the surface facing the right atrium). An atrial septumelectrode may also be an electrode that is directly or indirectlysecured to the atrial septum, but is spaced up to about 1, 2, or 4millimeters or more away from the septum, where the electric fieldproduced from the electrode is effective in stimulating the atrialseptum in substantially the same manner as an electrode inserted into orcontacting to the atrial septum. Patients treated by the methods of thepresent invention are typically human.

[0035] “Bachmann's bundle” as used herein refers to a transverse band ofmuscle fibers on the roof of the atria, immediately adjacent to or lyingalong side of the atrial septum.

[0036] The term “catheter” is used interchangeably with “lead” herein,and is not meant to imply that the particular structure has an interiorlumen for receiving a guide wire or the like, as such a lumen isoptional in carrying out the present invention, and the use of one ormore guidewires is optional in carrying out the present invention.

[0037] The term “concurrently”, when used herein with respect to two ormore defibrillation pulses, refers to pulses that are administeredsufficiently close in time so that the combined therapeutic effect isgreater than the sum of the therapeutic effects when the pulses areadministered singly. Such pulses may be administered simultaneously,partially overlapping in time, or sequentially in time. Whenadministered sequentially in time the pulses may or may not have anintervening time period therebetween. Preferably, the onset of asubsequent pulse occurs within 100, 200 or 500 milliseconds of theoffset of a preceding pulse.

[0038] The term “defibrillation pulse” is used herein to encompass anyof a variety of defibrillation, or cardioversion, waveforms. Theparticular type of pulse delivered is not critical and may, for example,comprise: a monophasic or biphasic waveform; a pulse that includes aseries of waveforms; waveforms that are uniform, stepped, saw-toothed,truncated exponential, etc.

[0039] The term “pulse generator” as used herein is intended toencompass any type of device, preferably contained within an implantablehousing to form an implantable cardioverter defibrillator (ICD), thatdelivers the defibrillation pulse or pulses desired to achieve aparticular method. In general, such pulse generators comprise a batterypower supply, a control circuit, and a capacitor (or capacitor circuit).The control circuit is connected to the battery and the capacitor forcharging the capacitor and delivering a therapeutic defibrillation pulsefrom the capacitor through the defibrillation electrodes. The controlcircuit typically includes a detection circuit for monitoring the heartof a subject and determining when the capacitor should be charged and atherapeutic pulse delivered. Numerous additional features may beincluded, as is known to those skilled in the art.

[0040] A. Atrial Septum Electrodes for Atrial Defibrillation.

[0041] As noted above, the present invention provides an implantablesystem for the defibrillation of the atria of a patient's heart. Such asystem typically comprises a first catheter configured for insertioninto the right atrium of the heart; a first atrial defibrillationelectrode carried by the first catheter and positioned at the atrialseptum of the heart; a second atrial defibrillation electrode whichtogether with the first atrial defibrillation electrode provides a pairof atrial defibrillation electrodes that are configured for orientationin or about the patient's heart to effect atrial defibrillation, and apulse generator operatively associated with the pair of atrialdefibrillation electrodes for delivering a first atrial defibrillationpulse to the heart of the patient. It will be appreciated that theatrial septum electrode need not be used in conjunction with every pulseor shock delivered by the system and methods as long as it used in someof the pulses or shocks delivered by the system and methods.

[0042]FIG. 1 illustrates a first embodiment of an implantable system ofthe present invention. The heart 20 is shown in partial cut-away view,with the right atrium 21, the right ventricle 22, and a portion of theleft atrium 23 being shown in cross section. The surface of the leftventricle 24 is shown so that veins or vessels 25 on the surface of theventricle that are accessed through the coronary sinus 26 (shown indashed lines) and the coronary sinus ostium 27 may be seen. A pair ofcatheters 30, 31, enter the heart through the superior vena cava 28. Onecatheter is positioned through a trans-septal puncture formed in theatrial septum so that the atrial septal electrode 32 that is connectedto that catheter extends through the septum. An introducer sheath,needle, or the like may be used to form the puncture and introduce theelectrode therethrough, as will be apparent to those skilled in the art.The other catheter extends through the ostium of the coronary sinus andthrough the coronary sinus and into a vessel on the surface of the leftventricle of the heart (e.g., the great vein), where an additionaldefibrillation electrode 33 connected to that catheter is positioned.

[0043] The system includes an implantable cardioverter defibrillator(ICD) 40 comprises a housing 41 containing a pulse generator 42, with asubcutaneous electrode 43 located on the external surface of the housingas described in U.S. Pat. No. 5,292,338 to Bardy. The defibrillator isthen implanted in the left or right (preferably left) thoracic region ofthe patient (e.g., subcutaneously, in the left pectoral region, inaccordance with known techniques. The housing electrode 43 may be usedin conjunction with or in alternative to other catheter mountedelectrodes.

[0044] Sensing of atrial fibrillation for triggering of a defibrillationcan be carried out through any suitable means, and may employ the sameelectrodes that are used for defibrillation or separate sensingelectrodes. In the alternative, the defibrillation pulse may, ifdesired, be triggered manually or externally by an operator or thepatient. It will be appreciated that a sensing electrode (not shown)will also preferably be provided in the right ventricle, e.g. on aseparate catheter, to sense the ventricular cycles and deliver thisinformation to the pulse generator so that the pulse generator deliversthe atrial defibrillation pulse or pulses at a time when ventricularfibrillation is not likely to be induced thereby, as is known in theart.

[0045] While the atrial septum electrode is primarily described hereinfor the delivery of atrial defibrillation or cardioversion pulses, itwill be appreciated that the system can be configured to carry out otheruseful methods from the atrial septum electrode. For example, an atrialseptum electrode can be used to deliver pacing pulses from the pulsegenerator prior to the onset of atrial fibrillation to reduce the chanceof atrial fibrillation occuring. In addition, an atrial septum electrodecan be used to deliver pacing pulses after the onset of atrialfibrillation, but before a defibrillation pulse is delivered, in aneffort to avoid the need to deliver a defibrillation pulse. Iffibrillation continues after the pacing pulse is delivered, then adefibrillation pulse can be delivered. The atrial septum electrode usedto deliver such pacing pulses may be the same or different from theatrial septum electrode used to deliver defibrillation pulses (e.g.,multiple adjacent atrial septum electrodes may be provided on a singlecatheter).

[0046]FIG. 2 illustrates a second embodiment of an implantable system ofthe present invention. This system again comprises a pair of animplantable ICD 50, a pair of catheters 51, 52, an atrial septumdefibrillation electrode 54, and an additional defibrillation electrode55 in the great vein. The atrial septum electrode is fixed to the atrialseptum by a terminal screw or helix 56 connected to the distal endportion of catheter 51, which penetrates partially into (or all the waythrough) the atrial septum. Of course, any suitable connecting means maybe employed in addition to a terminal screw or helix, including but notlimited to a retractable hook connected to the distal end portion of thecatheter 51.

[0047]FIG. 3 illustrates a third embodiment of an implantable system ofthe present invention, again including an implantable ICD 70, a pair ofcatheters 71, 72, and a defibrillation electrode 73 positioned in thegreat vein. The atrial septum electrode 74 is incorporated into anexpandable device or element 75 which is opened within the right atrium(or allowed to open within the atrium by removal of an introducer sheathor the like) to hold the electrode 76 against the atrial septum byexpanding to a size about the same as or slightly greater than theinterior diameter of the right atrium and forcing the electrode againstthe atrial septum. In the alternative, an expandable element could beused in conjunction with a helix, screw, hook or other fixing meanslocated on the distal tip of the catheter to unfold the electrode into aconfiguration contacting the atrial septum, to thereby provide bettercontact or expanded contact area of the defibrillation electrode againstthe atrial septum.

[0048]FIG. 4 illustrates a particularly preferred embodiment of animplantable system of the present invention, in which the catheter 90carrying the atrial septum electrode 91 is fixed to the catheter 92carrying coronary sinus electrode 93 to form a catheter assembly andfacilitate the holding of the atrial septum electrode against the atrialseptum. The system includes an ICD 94, which again may incorporatefeatures such as described in connection with ICDs as set forth above. Aconnecting member 95, typically located at the distal end portion of thefirst catheter and connected to the intermediate portion of the secondcatheter, is included for interconnecting the two catheters. Such aconfiguration or assembly, in addition to being particularly suitablefor carrying out the present invention has a variety of differentapplications, and is discussed in greater detail in section B below.

[0049] B. Catheter Assembly with Fixation of One Catheter to Another.

[0050] The present invention provides a catheter assembly useful for thedefibrillation or cardioversion of a patient's heart, of which theassembly illustrated in FIG. 4 is one example. As noted above, suchassemblies typically comprise a first transveneous catheter configuredfor insertion into the heart of the patient, the first transvenouscatheter having a proximal end portion, a distal end portion, and anelongate intermediate portion therebetween. The first transveneouscatheter typically has a first electrode connected thereto. The firstelectrode is typically connected to the first transveneous catheterintermediate portion, although it will be noted that the intermediateportion is quite elongate and the first electrode may be positionedanywhere along the length thereof.

[0051] A second transveneous catheter configured for insertion into theheart of the patient is also included in the assembly, the secondtransveneous catheter also having a proximal end portion, a distal endportion, and an elongate intermediate portion therebetween. The secondcatheter may, for example, be configured for positioning in a suitablelocation, such as into the right ventricle, optionally extending to theapex of the right ventricle, through the ostium of the coronary sinusand into or through the coronary sinus, etc. The assembly furtherincludes a connecting member attached to the first transveneous catheter(e.g., at the distal end portion or at the proximal portion thereof),with the connecting member connected to the second transveneous catheterintermediate portion.

[0052] The second transveneous catheter generally has at least oneelectrode connected thereto (. e.g., an electrode for positioning in thecoronary sinus or a vein on the surface of the left ventricle), whichelectrode may be a therapeutic, or defibrillation, electrode, and/or amonitoring electrode such as a ring electrode or tip electrode. However,the second transveneous catheter need not necessarily carry an electrodeif it functions primarily to secure or anchor the first catheter inplace. Hence, the second catheter may be referred to as an “anchoringcatheter” or “positioning catheter”.

[0053] While such catheter assemblies may be used for atrialdefibrillation systems and methods as described herein, it is alsoenvisioned that such catheter assemblies will find a variety ofadditional applications, such as for ventricular defibrillation orcardioiversion, whenever it is desirable to securely fix a particularcatheter in place.

[0054]FIG. 5 illustrates a catheter assembly 110 of the presentinvention, which may be configured in any suitable manner including butnot limited to that shown in FIG. 4. The assembly comprises a firstcatheter 111 having a proximal end portion, 112, a distal end portion113, and an elongate intermediate portion 114 therebetween. Note thatproximal end portions will typically terminate in a connector (notshown) to facilitate mechanical connection of the catheters to the ICDand electrical connection of the electrodes to the pulse generatorcontained therein. A first defibrillation electrode 115 is connected tothe intermediate portion 114. A connecting member 116 is connected tothe distal end portion 113 of the first catheter, and is permanentlyfixed to the second catheter 118 (e.g, by permanently fastening twoseparate members; by integrally forming the two members together).Second catheter 118 also has a proximal end portion 119, a distal endportion 120, and an intermediate portion 121, with a defibrillationelectrode 122 positioned proximal to the connecting member and a furtherdefibrillation electrode 123 positioned distal to the connecting member.As noted above, either or both of the electrodes on the second catheterare optional, and additional electrodes such as sensing electrodes couldbe included if desired.

[0055]FIG. 6 illustrates an alternate embodiment of a catheter assembly130 of the present invention, in which the first catheter 131 isreleasably fixed to second catheter 132 by means of a retractable loop133. Any suitable means can be used to retract the loop, such as theinsertion of a tendon 134 through a lumen in catheter 131 which connectsto the loop, and which can be drawn back to tighten the loop. As withany other such releasably secured connecting member, the loop can befastened around an intermediate portion 135 of the catheter assembly atany of a variety of locations to optimally configure the electrodeassembly for a particular patient. The intermediate portion 135 can besubstantially smooth as illustrated, or may be textured or the like toenhance fastening of the loop to the catheter and reduce lateralslippage along the length of the second catheter intermediate portion.If desired, an introducer sheath (not shown) can be deployed around thesecond catheter and used to push the loop forward down the secondcatheter until the desired location is achieved (e.g., just outside orproximal to the coronary sinus ostium, when the second catheter isinserted through the ostium), with the loop then being tightened and theintroducer sheath removed. In the alternative, an introducer can be usedto carry the second catheter to the desired position rather than pushthe connecting member to the desired position.

[0056]FIG. 7 illustrates a further alternate embodiment of a catheterassembly 150 of the present invention, in which the first catheter 151is releasably fixed to the second catheter 152 by means of an elasticloop 153. The elastic loop may be formed of any suitable polymericmaterial, metallic material or the like that is sufficiently resilientto allow its deformation and reformation around the second catheter(and, if necessary, around the first catheter). The distal end portion154 of the first catheter is enlarged to reduce the chance of theresilient loop slipping off the tip thereof (or, in the alternative orin addition thereto, the resilient loop could be permanently fastened tothe first catheter). As in the embodiment of FIG. 6, an introducersheath may be deployed around the second catheter to push the elasticloop to the proper location around the second catheter. Again, texturingor the like could be provided on the intermediate portion of the secondcatheter to reduce slippage along the length thereof.

[0057] In a variation to the embodiment described above in connectionwith FIG. 7, the fastening loop 153 could be substantially inelastic, ifthe second and/or first catheter itself were sufficiently elastic toallow the catheter to be forced therethrough, yet sufficiently resilientto secure the catheters to the loop when forced to the desired locationby means of an introducer sheath or the like.

[0058]FIG. 8 illustrates a still further embodiment of a catheterassembly 170 of the present invention, in which the connecting member (aretractable loop 171 with a tendon 172 as illustrated) is positioned onan intermediate portion 173 of the first catheter 174 rather than thedistal portion of the first catheter as shown above. Any number ofelectrodes could be included in such an embodiment. As illustrated, thefirst catheter 174 has electrodes 175, 176 proximal and distal to theconnector, and the second catheter 178 has electrodes 180, 181 proximaland distal to the loop connector. Such an assembly could be used, forexample, to position electrode 180 in or through the coronary sinus,electrode 176 in the right ventricle, electrode 175 at the atrialseptum, and electrode 181 in the right atrium or superior vena cava.

[0059]FIG. 9 illustrates a still further alternate embodiment of animplantable system comprising an ICD 190, and a pair of catheters 191,192 configured as an assembly through a connector 193. Here the secondcatheter extends into the right ventricle and is fixed to the apex ofthe right ventricle by means of a terminal screw or helix 194. Any otherterminal fastening means, such as a retractable hook, could also beemployed.

[0060]FIG. 10 illustrates a further embodiment of a catheter assembly210 of the present invention, comprising first and second catheters 211,212, and in which the second catheter includes an expandable stent 213that is expanded or retracted by tendon 214 to further anchor the secondcatheter within a suitable vessel, such as a pulmonary artery. Such anadditional anchoring feature could be added as appropriate to any of theembodiments described above.

[0061] C. Location of Additional Electrodes to Lower Shock Voltage andEnergy Required for Defibrillation.

[0062] A further aspect of the present invention is a method for thedefibrillation or cardioversion of the heart of a patient in needthereof while minimizing the voltage of defibrillation pulses to bedelivered. As noted above, the method involves, first, positioning firstand second defibrillation electrodes in operable association with theheart of the subject, the first and second defibrillation electrodesdefining a gradient field in the heart, the gradient field including aregion of the heart to be defibrillated. Next, a third electrode (e.g.,an atrial septum electrode) is positioned in the gradient field betweenthe first and second electrodes. Then, a first defibrillation pulsebetween the first and third electrode and a second defibrillation pulsebetween the second and third electrodes are concurrently delivered, withthe first and second defibrillation pulses together effective todefibrillate the heart. The voltage required for each of the first andsecond defibrillation pulses is preferably less than the voltagenecessary for a single defibrillation pulse delivered between the firstand second electrodes that is effective to defibrillate the heart. Allof the electrodes may be carried on transveneous catheters, eitherseparately or with multiple electrodes on a single catheter.

[0063] Such a technique can be used for any of a variety of purposes,including treating patients afflicted with atrial fibrillation andpatients afflicted with ventricular fibrillation. For atrialfibrillation, each of the first and second defibrillation pulses arepreferably not greater than, and more preferably less than, 50, 100, or150 volts in magnitude, and each of the first and second defibrillationpulses are preferably not greater than, and more preferably less than,one, two or four Joules in magnitude. Preferably, the gradient fieldcreated by the first defibrillation pulse and the second defibrillationpulse in the region of the heart to be defibrillated is at least 3 or 4volts per centimeter. The specific minimum potential gradient (whichmust be created throughout all, or substantially all, of thefibrillating myocardium), differs for different defibrillationwaveforms, but is thought to be in the range of approximatley 4 to 7volts per centimeter, with at least about a 4 volt per centimetergradient needed for a good biphasic defibrillation waveform.

[0064] FIGS. 11A-C schematically illustrates such a technique. Panel Aillustrates an original pair of electrodes (A and B) that create asubstantially even potential gradient field in the region between thetwo electrodes, with the gradient field including a region in the atriaor ventricles or the heart of a patient to be defibrillated. Assumingthat (1) the electrodes are 20 cm apart, (2) the conductivity of themedium is substantially uniform, and (3) there is no substantial voltageloss at the electrode-media interface, and (4) a 4 volt per centimeterpotential gradient must be created throughout the region, then a shockvoltage of about 80 volts will be required. Panel B shows a thirdelectrode (C) approximately half way between the original pair ofelectrodes (A,B). A shock between electrodes A and C will create apotential gradient of 4 volts per centimeter in the left half of theregion with a 40 volt shock. Similarly, a 40 volt shock betweenelectrodes C and B will create the desired 4 volt per centimeterpotential gradient throughout the right half of the region. If the twoshocks are given concurrently and are substantially the same duration asthe original shock through electrodes A and B, then the voltage of eachshock will be approximately half that of the original, while the totalenergy of the two shocks will be the same as that of the original shock.Therefore, the maximum voltage delivered to the heart of the patient inthis example will be about 40 volts rather than 80 volts.

[0065] More than three electrodes may be used to implement thistechnique. For example, panel C of FIG. 11 shows the addition of twoadditional electrodes (D and E). Concurrent (e.g., sequential) shocksthrough four pairs of electrodes (A to D, D to C, C to E, and E to B) invarious sequences will again reduce the voltage in half to 20 voltswhile maintaining the same total energy.

[0066] When this technique is used for atrial defibrillation, such aswith a system and/or catheter assembly as illustrated in connection withFIGS. 1-10 above, the method may comprise the steps of: (a) positioninga first defibrillation electrode in the right atrium (including theright atrial appendage), superior vena cava or right ventricle of thesubject; (b) positioning a second defibrillation electrode in thecoronary sinus or a vein on the surface of the left ventricle of theheart (e.g., the great vein); (c) positioning a third electrode at theatrial septum of the heart; and then (d) concurrently delivering (i) afirst defibrillation pulse between the first and third electrode and(ii) a second defibrillation pulse between the second and thirdelectrodes. Preferably, each of the first and second defibrillationpulses has an energy not greater than, or less than, one, two or fourJoules, preferably each of the first and second defibrillation pulseshas a voltage less than 50, 100 or 150 volts, preferably the first andsecond defibrillation pulses are delivered within 500 milliseconds ofeach other, and preferably the gradient field created by eachdefibrillation pulse in the heart of the patient is greater than 4 voltsper centimeter.

[0067] The foregoing method of reducing shock voltage may be implementedin techniques other than atrial defibrillation. For example, FIG. 12schematically illustrates a technique for lowering ventriculardefibrillation threshholds during open-chest cardiac surgery with anarray of three or more epicardial electrodes. The particular electrodearray of FIG. 12 is similar to the array of FIG. 11C. Such a systemdecreases the voltage needed for defibrillation in the operating room,which could decrease the damaging effects associated with largedefibrillation shocks. Since the electrodes in FIG. 12 are placed on theepicardium, they will not have as much effect on the shock potentialgradient field in the ventricular septum as they will in the ventricularfree walls. A modification of this system to increase the potentialgradient in the septum is, accordingly, to add an additional electrode(F) place in the right ventricular cavity against the inter-ventricularseptum, optionally as part of a catheter. Then, in addition to thevarious possible concurrent shock sequences through electrodes A to E,one or more shocks could be delivered from electrode F to some or all ofelectrodes A to E. Systems for implementing such methods can be providedwith the necessary electrodes operably associated with a pulse generatorconfigured or programmed to carry out the shock patterns describedherein in accordance with known techniques.

[0068] The implementation of the present invention in connection with aBachmann's bundle electrode is further illustrated in connection withFIGS. 16-18, where “RA” means right atrium, “RV” means right ventricle,“LA” means left atrium, “LV” means left ventricle, “SVC” means superiorvena cava, “CSos” means ostium of the coronary sinus, and “Distal CS”means distal coronary sinus. Therapeutic pulses and other electrodes maybe implemented as described above in connection with atrial septumelectrodes.

[0069] For example, as shown in FIG. 16, defibrillation may be carriedout with two shocks or defibrillation pulse, with one of the shocksdelivered from an electrode 301 at the right atrium to the distalcoronary sinus 303, and the other delivered from an electrode 302 atBachmann's bundle, near or adjacent the anterior-superior insertion ofthe atrial septum, to an electrode 304 in or adjacent the coronary sinusostium (os), near the posterior-inferior insertion of the atrial septum.The electrode at the os of the coronary sinus can be on the samecatheter 305 that contains the electrode in the distal coronary sinus.The electrode at Bachmann's bundle can be on its own lead 306. The rightatrial electrode can either be on its own lead, or on the lead passinginto the coronary sinus.

[0070] The first of the two shocks can be either through the rightatrial to distal coronary sinus electrodes or through the Bachmann'sbundle to coronary sinus os electrodes. The voltage of the second shockcan be (1) equal to the trailing edge voltage of the first shock as froma single capacitor, (2) equal to the leading edge voltage of the firstshock, as would occur if each shock were delivered from a differentcapacitor charged to the same voltage, or (3) with the voltage of thesecond shock some other fraction of the voltage of the first shock, ascould be performed with two capacitors charged to different voltages.All three of these cases can be delivered from a single capacitor bankby using an electronic circuit to cause the voltages of the first andsecond shock to be the desired values. For example, atrialdefibrillation with such electrode configurations may be carried outwith less than 200 or 300 volts, while the capacitor bank in anatrial-ventricular defibrillator can be charged to approximately 800volts since this voltage is required for ventricular fibrillation. Anelectronic control circuit can shape the waveform delivered from the 800voltcapacitor to be almost any desired shape for two different shockseach of which are less than 200 or 300 volts.

[0071] Note that the insertion of the superior vena cava into the rightatrium is near Bachmann's bundle. Therefore another shock configurationis to substitute an electrode in the superior vena cava for theelectrode at Bachmann's bundle, e.g., to stimulate Bachmann's bundle.The advantage of this configuration for an atrial-ventriculardefibrillator is that the superior vena cava electrode is alreadypresent for delivering shocks to halt ventricular arrhythmias. Possiblelead configurations using the electrode in the superior vena cava areshown in FIGS. 17-18. As illustrated in FIG. 17, such an embodiment maycomprise a first catheter 315 carrying a right atrium electrode 311, acoronary sinus os electrode 314, and a distal coronary sinus electrode313 as described above, and a second cathter or lead 316 carrying asuperior vena cava electrode 312 and an optional right ventricleelectrode 317 (which may be used for atrial or ventriculardefibrillation). Still another embodiment, as illustrated in FIG. 18, anembodiment may comprise a first catheter 325 carrying a coronary sinusos electrode 324 and a distal coronary sinus electrode 323 as describedabove, a second catheter or lead 326 carrying a superior vena cavaelectrode 322 and an optional right ventricle electrode 327 (which maybe used for atrial or ventricular defibrillation), and a third catheteror lead 328 carrying a right atrial electrode 321 (which third catheter328 may or may not be attached to first catheter 325 in the mannerdescribed in connection with FIG. 10 above). One preferred embodiment ofthe shocks would be right atrium to distal coronary sinus, followed bysuperior vena cava to coronary sinus ostium. Another configuration wouldbe with these two shocks in reverse sequence.

[0072] Another catheter device that may be used in carrying out thepresent invention is a flexible, two-pronged catheter 350, which may beused for (among other things) situating electrodes such asdefibrillation electrodes in the right atrium, the coronary sinus, andalong the right side of the atrial septum (or Bachmann's bundle). Thedevice, schematically illustrated in FIG. 19, is comprised of a primarycatheter body 351 that has lead body (preferably coil) electrodes 352,353, 354; the distal electrode 354 may be used for situation orinsertion into the coronary sinus, and the proximal electrode 352 may beused for situation in the right atrijum. The electrode 353 (SP) carriedby an appendage catheter body 360 connected to the primary catheter body351, may be used for situation along the right side of the atrial septumor Bachmann's bundle, and is connected to the primary catheter body midportion, preferably between the electrodes 352, 354, and in oneembodiment approximately half way between electrodes 352 and 354. ThisSP electrode may take one of several forms. The appendage catheter body360 is connected to the primary catheter body 351, at a junction portion362 that has a memory and corresponding elasticity such that the angle363 between the primary catheter body 351 and the appendage catheterbody 353 is about 30, 50 or 70 to 120, 140 or 160 (most preferably about90) degrees off of the primary catheter body. But, the elongateconnector has elasticity at its cfonnection portion with the primarycatheter such that the SP electrode may be bent back in line(substantially parallel) with the primary catheter. In this manner, theSP electrode may be bent along the primary catheter for transvenoussituation of the catyheter system into the heart, for example byinsertion through an introducer tube or guide. For extraction, the SPelongate member may also be elastically bent back in the oppositedirection along the axis of the primary catheter toward the CSelectrode.

[0073] The SP electrode may take one of several forms. A simpleembodiment is a lead-body coil electrode, as found in ICD lead-bodydefibrillation electrodes. In this embodiment the inner diameter of theintroducer required to situate the catheter system must be equal to atleast the sum of the diameters of the SP coil and primary catheter. Inan alternate embodiment, the SP electrode may be a relatively flat meshelectrode. This flat mesh electrode may be of a length as desired (e.g.,1 to 6 cm). Its width may be up to (for example) the circumference ofthe primary catheter. Being pliable, during placement of the cathetersystem, the SP electrode may be bent back over the proximal side of theprimary catheter, and the SP electrode may be “wrapped” around theprimary catheter, thereby requiring an introduce with an inner diameterthat is not substantially greater than that which would be employedwithout the SP member.

[0074] While the connecting portion of the SP member attchement to theprimary catheter has elasticity, the primary catheter body hasrotational stiffness so that, once in the general vicinty, the prximalend of the catheter may be rotated to optimize the position of the SPelectrode. Further, the material connecting the SP elongate member tothe primary catheter may be made of a memory alloy, polymer, orcomposite thereof, or the like, such that it maintains the desired angleas noted above relative to the long axis of the primary catheter. Also,an optional pacing tip electrode 364 may be placed at the tip of the SPelongate member, so that the pacing of the atrial septum or Bachmann'sBundle may be performed.

[0075] The present invention may be implemented in combination with, oremploying the features of, numerous additional methods and systems forthe defibrillation and cardioversion of a patient's heart, including butnot limited to those disclosed in U.S. Pat. No. 6,006,131 to Cooper etal.; U.S. Pat. No. 6,002,962 to Huang et al.; U.S. Pat. No. 5,987,354 toCooper et al.; U.S. Pat. No. 5,978,705 to Ideker et al.; U.S. Pat. No.5,978,704 to Ideker et al. U.S. Pat. No. 5,509,925 to Adams; U.S. Pat.No. 5,630,834 to Bardy; and U.S. Pat. No. 5,476,499 to Hirschberg. Thedisclosures of all U.S. Patent references cited herein are to beincorporated herein by reference in their entirety.

[0076] The present invention is further illustrated in the experimentalexamples set forth below.

EXAMPLES Reduction of Atrial Defibrillation Threshold with anInteratrial Septal Electrode

[0077] This example demonstrates that an electrode configuration with aninteratrial septal electrode placed approximately midway between theright atrial appendage and coronary sinus electrodes increases thepotential gradient in this region and thus lowers the atrialdefibrillation threshold (ADFT).

[0078] I. METHODS

[0079] All studies were performed in accordance with the guidelinesestablished in the Position of the American Heart Association onResearch Animal Use adopted by the American Heart Association on Nov.11, 1984.

[0080] Of 11 adult sheep, 8 (41±6 kg, heart mass 217±8 g) completed theexperimental protocol; only data from these 8 animals were compiled.

[0081] Animal Preparation. As a preanesthetic agent, a 1-to-1 mixture oftiletamine and zolazepam (8-10 mg/kg) was given intramuscularly. About10 minutes later, thiopental (2-6 mg/kg) was administered as a slowintravenous bolus. The animal was laid in a dorsally recumbent positionon a fluoroscopy table, intubated, and placed on a volume-cycledventilator (tidal volume: 15-20 ml/kg) with a 4% isoflurane/oxygenmixture at a rate of 8-12 breaths per minute. The isofluraneconcentration was decreased to 1.5-3.5% to maintain a deep surgicalplane of anesthesia. Ventilator settings were adjusted as necessary tocorrect for respiratory acidosis or hypoxemia. Intravenous fluids(Lactated Ringer's solution) were infused throughout the experiment withsupplemental electrolytes as needed as determined by serial blood gasand chemistry analyses conducted every 30-60 minutes.

[0082] An 8 Fr. sheath was placed in the left femoral arterypercutaneously for continuous arterial pressure monitoring. The animalwas instrumented for lead II ECG and esophageal temperature monitoring.A heated water blanket was used to maintain body temperature at 37±1° C.Neuromuscular blockade was achieved with a 1 mg/kg succinylcholinechloride intravenous bolus followed by an intravenous drip (5-8 mg/min)for maintenance, depending upon neuromuscular tone. At all times, anexternal defibrillator with external paddles was available in the eventof non-perfusing ventricular tachyarrhythmia.

[0083] Defibrillation Catheter Placement. All catheters were positionedtransvenously under fluoroscopic guidance. Through a jugular vein, adefibrillation lead (Perimeter #7109, Guidant Corp., St. Paul, Minn.)with a distal 6-cm long electrode was situated with its coil electrodein the distal coronary sinus (CS) along the left lateral heart and itstip under the left atrial appendage. Care was taken to not place thislead in the persistent superior vena cava, which is present in thisspecies. A modified quadripolar catheter (Mansfield EP-Boston ScientificCorp., Watertown, Mass.) with a 3.5-cm-long coil electrode 1 cm proximalto the catheter tip was positioned in the right atrial appendage (RAA)through the left femoral vein. The coil electrode was laid along thesuperior wall of the RAA. The bipolar tip of this catheter was used forthe burst-pacing induction of AF. Another two 3.5-cm-long coil electrodecatheters were also placed in the main and left pulmonary artery (PA)and lower right atrium (LRA), respectively. The LRA electrode waspositioned at the junction of right atrium and inferior vena cava.

[0084] A custom-made 6-cm coil electrode that served as the interatrialseptal electrode (SP) was constructed along a catheter; the distal endof the electrode was 3 cm from the catheter tip. It was situated througha trans-septal procedure. An 8 Fr. Mullins sheath was advanced into theright atrium through the right femoral vein over a 0.038″ guide wire.Then, a Brockenbrough needle replaced the guide wire and was displacedthrough the atrial septum, usually under LAO projection. Confirmation ofleft atrial catheterization was made by measurement of oxygen saturationof blood withdrawn through the Brockenbrough needle and with contrastinjection into the left atrium during fluoroscopy. A stiff 0.038″ guidewire was positioned in the left atrium through the sheath. The Mullinssheath was then withdrawn over the wire, leaving the wire in the leftatrium. Next, an 11 Fr. guide sheath was advanced over the wire and intothe left atrium. After withdrawal of the dilator and guide wire, theseptal electrode was inserted into the left atrium through the guidesheath. The tip of the septal electrode catheter was placed against thelateral wall of left atrial appendage. About ⅔ of the electrode was inthe left atrium and ⅓ in the right atrium. After the septal electrodewas in position, 1000 units of heparin were given intravenously everyhour.

[0085] Additionally, a three-electrode defibrillation catheter (EndotakDSP, Guidant Corp., St. Paul, Minn.) was introduced into the rightventricle through the other jugular vein; the two lead-body coilelectrodes from this catheter were situated in the right ventricle (RV)and superior vena cava (SVC). The tip electrode from this catheter wasused for ventricular pacing. A three-wire subcutaneous array (SQA) wasinserted over the left side of the heart. In the event of ventriculartachyarrhythmias, the electrode configuration for ventriculardefibrillation was RV as the first phase anode with CS, SVC and SQAelectrically common as the first phase cathode (RV→CS+SVC+SQA).

[0086] Induction of Atrial Fibrillation. To allow AF to be maintained,acetyl-β-methylcholine chloride (Sigma Chemicals Co., St Louis, Mo.) wascontinuously infused into the pericardium. The pericardial space wasapproached percutaneously under fluoroscopic guidance with a 3-inch-long16-gauge needle from just inferior to the right subxiphoid position withthe animal turned about 20 degrees toward the right side. When theneedle was confirmed to be within the pericardial space by contrastinjection, a guide wire was gently inserted within the needle into thepericardial space. The pericardial location for the guide wire wasconfirmed by inability to move it outside the fluoroscopic image of theheart silhouette. After removal of the needle, a 6 Fr. sheath wasadvanced into the pericardial space over the wire. After flushing withacetyl-β-methylcholine chloride, a 4 Fr. pig-tail catheter was insertedthrough the sheath. Typically, the catheter tip was advanced to near theleft atrial appendage and the sheath was removed.

[0087] Acetyl-β-methylcholine chloride solution (1 g/250 ml saline) wasinfused at a rate of 20 μL/min using a micro-infuser. Burst pacing usedto induce AF consisted of 2-ms stimuli delivered at intervals of 30-60ms. AF was defined as irregular rapid atrial activity with an irregularventricular response on the ECG. Blood pressure and heart rate wererecorded before and 20 min after acetyl-β-methylcholine infusion.

[0088] Defibrillation Waveforms and Lead Configurations. Onceacetyl-β-methylcholine chloride was infused long enough to support AFmaintenance of >10 minutes (typically ˜20 minutes), the defibrillationprotocol was begun. The waveform generation system has been describedpreviously (R. Cooper et al., Circulation. 1997;96:2693-2700). Briefly,a monophasic waveform was produced by a programmable defibrillator(HVS-02, Ventritex, Inc). This monophasic waveform was divided into abiphasic, truncated-exponential waveform by a high-voltage, cross-pointswitch; for sequential shocks, two biphasic, truncated-exponentialwaveforms were created with the use of an additional pair of cross-pointswitches. Each biphasic waveform had a first-phase duration of 3 ms anda second-phase duration of 1 ms. The interval between each phase of thebiphasic waveforms and between the two biphasic waveforms of sequentialshocks was 20 μsec. Because all stimuli (single or sequential shocks)were produced from the output of one defibrillator, all phases of thewaveforms exhibited decaying voltage from a single capacitor, in whichthe trailing-edge voltage of each preceding phase was equal to theleading-edge voltage of the succeeding phase.

[0089] In each animal, the ADFTs of five test configurations weredetermined (Table 1). Three configurations utilizing the septalelectrode were named A1, A2 and A3. The two others were named B and C,respectively. The order of determining the test-configuration ADFTs wasrandomized in each animal as follows. The order among A, B and C wasinitially randomized, and then the order of A1, A2 and A3 (within A) wasrandomized. The ADFTs of the configurations utilizing the septalelectrode were measured consecutively in order to obviate the need forrepositioning this electrode. During the ADFT testing of anyconfiguration, passive electrodes not delivering any shock for thatconfiguration were removed. To minimize the likelihood of ventriculartachyarrhythmia induction, shock delivery was synchronized toright-ventricular pacing, which triggered the Ventritex defibrillatorand cross-point switches via custom software on a Macintosh Computer.The cycle length of this pacing was 250-400 ms, depending on theventricular rate during AF. Shocks were delivered 20 ms after the 8^(th)pacing pulse. TABLE 1 Test Configurations First Shock Second ShockBiphasic Anode Cathode Anode Cathode Waveform A1 RAA + CS SP Single A2RAA SP CS SP Sequential A3 CS SP RAA SP Sequential B RAA CS Single C RAACS LRA PA Sequential

[0090] The ADFT of each test configuration was determined using amultiple-reversal method with an initial starting peak voltage of 100 Vand step sizes of 40/20/10 V. If the initial shock failed, the next andsubsequent shock voltages were increased by 40 V until a shocksucceeded. Following the first shock that successfully terminated AF,the voltages of subsequent shocks were decreased by 20 V until a shockfailed. Then the shock voltages were increased by 10 V until a shocksucceeded again. Conversely, if the initial shock succeeded, subsequentshock voltages were decreased by 40 V until a shock failed. Then shockvoltages were increased by 20 V until a shock succeeded, after whichshock voltages were decreased by 10 V until a shock failed again. Thelast successful shock of the third reversal was deemed the ADFT of thetest configuration. Before starting the defibrillation protocol, 3-5test shocks were given. All test shocks were delivered after inducing AFand allowing it to be sustained 1 minute. When a test shock failed, arescue shock of 200-300 V was given. A 1-2 min period of sinus rhythmwas allowed before the next induction of AF.

[0091] Data Acquisition. The leading-edge (peak) voltage and current ofeach test shock were recorded, and the impedance and delivered energy ofeach shock were computed by a waveform analyzer (DATA 6100, DataPrecision).

[0092] Postmortem Examination. After the completion of data collection,euthanasia was induced with an intravenous bolus of potassium chloride.The chest was opened and the location of the electrodes of the last testconfiguration was confirmed by palpation through the heart walls. Theheart was then removed. The great vessels were trimmed to the point ofinsertion into each cardiac chamber, and the pericardium was removed.The mass of the heart was determined.

[0093] Statistical Analysis. Results are expressed as the mean±SD. Theoverall effect of the 5 test configurations on each ADFT characteristicwas tested by repeated-measures ANOVA. Pair-wise differences in measuresbetween the 5 configurations were tested by paired t tests. A value ofP<0.05 was considered significant.

[0094] II. RESULTS

[0095] Reproducible, sustained AF could be induced in all animals. Theventricular rate in sinus rhythm before and 20 min after administrationof acetyl-β-methylcholine was similar (112±8 vs. 109±11 beat/min,respectively, P=NS). The drug significantly lowered the sinus-rhythmsystolic/diastolic blood pressure, however (107±8/83±4 vs. 84±7/62±5mmHg, P<0.05). During AF, the ventricular rate varied from 80 to 178beat/min (131±36 beat/min). After successful test shocks, sinus rhythmusually recovered quickly (<1.5 sec). In 1 sheep with a long sinusrecovery time (>2-4 sec), temporary post-shock atrial pacing wasperformed.

[0096] Leading Edge Voltage. The ADFT leading-edge-voltage of the 5configurations is shown in FIG. 13. The ADFT leading-edge-voltage ofconfiguration A2 (RAA→SP/CS→SP; 71±16 V) was significantly lower thaneach of the other 4 configurations (A1: 102±36 V; A3: 121±34 V; B:156±38 V; and C: 96±29 V). The ADFT leading-edge-voltage ofconfiguration B (RAA→CS) was significantly higher than the other 4configurations.

[0097] Leading Edge Current. The ADFT leading-edge-current is shown inFIG. 14. The ADFT leading-edge-current of configuration A2 (1.68±0.48 A)was significantly lower than that of the other 4 configurations A1, A3,B and C (A1: 4.32±1.59 A; A3: 3.61±1.28 A; B: 2.99±1 A; and C: 1.92±0.65A). The ADFT leading-edge-current of configuration C was lower than thatof configurations A3 and B. The leading-edge-current ADFT ofconfiguration A1, which was the sum of the currents of two pathways:RAA→SP and CS→SP, was higher than that of configurations A2, B and C butnot configuration A3.

[0098] Impedance. The impedances of the test configurations are shown inTable 2. Impedances of the same pathway in different test configurationswere not significantly different. Configuration A1 exhibited the lowestimpedance, which was approximately the reciprocal of the sum of thereciprocal impedances of its two pathways (RAA→SP and CS→SP) asestimated from individual shocks across these pathways during sequentialshocks.

[0099] Shock Energy. The ADFT shock-energy of the 5 configurations isshown in FIG. 15. Configuration A2 had a significantly lower ADFTshock-energy than each of the other 4 test configurations (A2: 0.39±0.17J vs. A1: 0.86±0.59 J, A3: 1.16±0.72 J, B: 1.27±0.67 J, and C: 0.68±0.46J; P<0.05 for each comparison). The ADFT shock-energy of configurationA2 was lower than that of configurations A1, A3, B and C by 46±20%,63±14%, 68±8%, and 36±15%, respectively. Configuration C had a lowerADFT shock-energy than configurations A1, A3 and B (P<0.05 for eachcomparison). Compared with configuration B, configuration C reducedshock energy by 50±9%. Configuration A1 had a lower ADFT shock-energythan configuration B (37±15% lower, P<0.05), but not than configurationA3. The difference in ADFT shock-energy between configurations A3 and Bwas not significant. TABLE 2 Impedances of all the current pathwaysCurrent Pathways Impedance(Ω) A1 Single RAA + CS → SP 25 ± 3 A2 FirstRAA → SP 46 ± 3 Second CS → SP 34 ± 4 A3 First CS → SP 35 ± 4 Second RAA→ SP 45 ± 4 B Single RAA → CS 54 ± 6 C First RAA → CS 54 ± 7 Second LRA→ PA 49 ± 4

[0100] While care must be used in directly extrapolating the results ofthis study to humans because of the particular pharmaceuticalinterventions employed. Nevertheless, this study demonstrates that, inan acute sheep model of sustained AF, atrial defibrillationconfigurations utilizing an additional electrode at the interatrialseptum were more efficacious than the present standard configuration bywhich cardioversion is achieved with RAA→CS. The ADFT shock-energy ofRAA+CS→SP was 37±15% lower, and sequential shock configurationRAA→SP/CS→SP was 68±8% lower than that of RAA→CS.

[0101] The foregoing is illustrative of the present invention, and isnot to be construed as limiting thereof. The invention is defined by thefollowing claims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. An implantable system for thedefibrillation of the atria of a patient's heart, said systemcomprising: a first atrial defibrillation electrode configured forstimulating Bachmann's bundle and for positioning on or adjacentBachmann's bundle along the superior aspect of the atrium and adjacentto the atrial septum; a second atrial defribrillation electrode whichtogether with said first atrial defibrillation electrode provides a pairof atrial defibrillation electrodes; and a pulse generator operativelyassociated with said pair of atrial defibrillation electrodes fordelivering an atrial defibrillation pulse.
 2. The implantable systemaccording to claim 1, wherein said first atrial defibrillation electrodeis carried by a first catheter, said first catheter configured forinsertion into the right atrium of said heart without extending into theright ventricle of said heart.
 3. An implantable system according toclaim 1, wherein the electrode is configured to be positioned within atrans-septal puncture in the atrial septum or in Bachmann's bundle. 4.An implantable system according to claim 1, wherein said first atrialdefibrillation electrode is carried by a first catheter, said firstcatheter has a distal end portion and a terminal screw connected to thedistal end portion, whereby said first electrode may be fixed to saidatrial septum or Bachmann's bundle with said terminal screw.
 5. Animplantable system according to claim 1, wherein said first atrialdefibrillation electrode is carried by a first catheter, and said firstcatheter has a distal end portion and a retractable hook connected tosaid distal end portion, whereby said first electrode may be fixed tothe atrial septum or Bachmann's bundle with said hook.
 6. An implantablesystem according to claim 1, wherein said first atrial defibrillationelectrode is carried by a first catheter, said first catheter having adistal end portion and an expandable member connected to said distal endportion, with said first electrode connected to said expandable member.7. An implantable system according to claim 1, further comprising asecond catheter configured for insertion through the coronary sinus andinto a vein on the surface of the left ventricle of the heart, whereinsaid second electrode is connected to the second catheter.
 8. Animplantable system according to claim 1, further comprising animplantable housing having an external surface portion, with said pulsegenerator contained within the housing, and with the second electrodeconnected to the external surface portion of the housing.
 9. Animplantable system according to claim 1, further comprising a secondcatheter, with said first catheter connected to said second catheter.10. An implantable system according to claim 9, wherein said secondcatheter is configured for positioning in the right ventricle orcoronary sinus of said heart.
 11. A method for the defibrillation of theatria of a patient's heart, said method comprising: positioning a firstatrial defibrillation electrode on or adjacent Bachmann's bundle alongthe superior aspect of the atrium and in or adjacent to the atrialseptum for stimulating Bachmann's bundle; positioning a second atrialdefribrillation electrode to provide a pair of atrial defibrillationelectrodes together with said said first atrial defibrillationelectrode; and administering an atrial defibrillation pulse through saidpair of atrial defibrillation electrodes.
 12. The method according toclaim 11, wherein said first atrial defibrillation electrode is carriedby a first catheter, and said first catheter is inserted into the rightatrium of said heart without extending into the right ventricle of saidheart.
 13. The method according to claim 11, wherein the said firstatrial defibrillation electrode is positioned within a trans-septalpuncture in the atrial septum or in Bachmann's bundle.
 14. The methodaccording to claim 11, wherein said first atrial defibrillationelectrode is carried by a first catheter, said first catheter has adistal end portion and a terminal screw connected to the distal endportion, and said first atrial defibrillation electrode is fixed to theatrial septum with said terminal screw.
 15. The method according toclaim 11, wherein said first atrial defibrillation electrode is carriedby a first catheter, and said first catheter has a distal end portionand a retractable hook connected to said distal end portion, and saidfirst atrial defibrillation electrode is fixed to the atrial septum orBachmann's bundle with said hook.
 16. The method according to claim 11,wherein said first atrial defibrillation electrode is carried by a firstcatheter, said first catheter having a distal end portion and anexpandable member connected to said distal end portion, with said firstelectrode connected to said expandable member, and said first atrialdefibrillation electrode is positioned by expanding said expandablemember.
 17. The method according to claim 11, further comprisinginserting a second catheter through the coronary sinus and into a veinon the surface of the left ventricle of the heart, wherein said secondelectrode is connected to said second catheter.
 18. The method accordingto claim 11, further comprising inserting a second catheter into saidsubject, with said first catheter connected to said second catheter. 19.The method according to claim 18, wherein said second catheter ispositioned in the right ventricle or coronary sinus of said heart.
 20. Atransveneous catheter for stimulating the heart of a patient at separatelocations therein, said catheter comprising: a catheter body having aproximal portion, an intermediate portion and a distal portion; a firstelectrode connected to said catheter body distal portion; a catheterappendage having a proximal portion and a distal portion said appendageproximal portion connected to said catheter body intermediate portion;and a second electrode connected to said appendage distal portion.
 21. Atransveneous catheter according to claim 20, wherein said catheter bodyis configured for insertion into the right ventricle of the heart.
 22. Atransveneous catheter according to claim 20, wherein said catheter bodyis configured for insertion through the coronary sinus ostium and intothe coronary sinus of the heart.
 23. A transveneous catheter accordingto claim 20, wherein said second electrode is an aterial electrode. 24.A transveneous catheter according to claim 20, wherein said secondelectrode is an atrial septum electrode.
 25. A transveneous catheteraccording to claim 20, wherein said second electrode is a Bachmann'sbundle electrode.
 26. A method for the defibrillation of the atria of apatient's heart, comprising the steps of: providing a set of atrialdefibrillation electrodes for defibrillating said patient's heart, saidset including a first atrial defibrillation electrode positioned in thesuperior vena cava of said patient; delivering a first defibrillationpulse to the atria of said heart, and then delivering a seconddefibrillation pulse to the atria of said heart, wherein at least one ofsaid first and second defibrillation pulses is delivered with said firstatrial defibrillation electrode.
 27. A method according to claim 26,said set of atrial defibrillation electrodes further comprising a secondatrial defibrillation electrode positioned in the coronary sinus of saidheart, and wherein at least one of said first and second defibrillationpulses is delivered with said second atrial defibrillation electrode.28. A method according to claim 27, wherein at least one of said firstand second defibrillation pulses is delivered between said first andsecond defibrillation electrodes.
 29. A method for defibrillating theatria of a patient's heart, comprising: delivering a firstdefibrillation pulse to the atria of said heart, and then delivering asecond defibrillation pulse to the atria of said heart, and wherein theleading edge peak voltage of said second defibrillation pulse is atleast 95% of the leading edge peak voltage of said first defibrillationpulse.
 30. A system for defibrillating the atria of a patient's heart,comprising: a pulse generator configured for delivering a firstdefibrillation pulse to the atria of said heart, and then delivering asecond defibrillation pulse to the atria of said heart, wherein theleading edge peak voltage of said second defibrillation pulse is atleast 95% of the leading edge peak voltage of said first defibrillationpulse.